Nutritional Bioavailability of Manganese - American Chemical Society

Chapter 7

Iron in Manganese Metabolism N. Gruden Institute for Medical Research and Occupational Health, M. Pijade 158, 41001 Zagreb,

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Yugoslavia

The interaction of iron and manganese was studied on intact white neonatal and weanling rats, and on the everted intestinal segment of adult rats. The stimulating effect of milk diet on manganese absorption was eliminated by addition of iron to milk. This inhibition of manganese absorption leveled off above 5 mg Fe/100 ml milk. It was observed after one day of feeding on iron supplemented milk and disappeared on the fourth day after withdrawing the supplementary iron. Manganese retention in the intestinal wall was far less affected by iron than its transport. The competition between iron and manganese absorption is is not yet developed in neonates but develops rather abruptly in the third week of rat's life. To function properly this competitive mechanism needs to be set either by iron pretreatment or by a higher iron dose. It has been recognized for a long time that there area large number of interactions among trace elements with possible profound metabolic consequences (1,2). The knowledge about the physiological functions and optimum intake of trace elements should therefore be considered in the light of interactions between themselves and with the other elements. There are various mechanisms by which such interactions may take place, like chemical association, competition for a binding ligand-carrier, metabolic changes, membrane alteratios. The result is usually that one elements inhibits the metabolic action of another, but the two can also act sinergistically, causing a effect greater than either element causes alone. The situation is frequently rather complex, with an interactions between metals in a chain of reactions C3). The subject has been appreciated by many nutritionists. However, for different reasons, the knowledge pertinent to humans has been developing rather slowly (4). Further research may reveal that such interactions are of greater consequence to human health than it is now generally acknowledged. We focus here our attention to the action of iron on manganese metabolism, i.e. on the two most studied essential trace elements. 0097-6156/87/0354-0067$06.00/0 © 1987 American Chemical Society

Kies; Nutritional Bioavailability of Manganese ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


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We s h a l l a l s o b r i e f l y t o u c h upon the e f f e c t of i r o n on cadmiummanganese i n t e r a c t i o n . The importance of manganese as an e s s e n t i a l d i e t a r y component is well established. I t i s i n t e r e s t i n g to n o t e t h a t f o r 25 y e a r s a f t e r i t s e s s e n t i a l i t y was r e c o g n i z e d , manganese has been t r e a t e d as the t r a c e element of p u r e l y academic i m p o r t a n c e . Nowadays i t i s a feed a d d i t i v e . Manganese d e f i c i e n c y r e s u l t s i n a wide v a r i e t y of s t r u c t u r a l , p h y s i o l o g i c a l and b i o c h e m i c a l d e f e c t s , f o r i t has been i m p l i c a t e d i n a number o f m e t a b o l i c and e n z y m a t i c p r o c e s s e s ( 5 - 1 5 ) . Hurley has summarized the e v i d e n c e t h a t manganese i s e s s e n t i a l f o r normal p r e n a t a l and n e o n a t a l development, w i t h d e f i c i e n c y r e s u l t i n g i n a v a r i e t y of c o n g e n i t a l m a l f o r m a t i o n s ( 1 6 ) . Manganese i s a l s o a t o x i c a g e n t , though i t can be r e g a r d e d as one o f the l e a s t t o x i c t r a c e e l e m e n t s . A wide m a r g i n of s a f e t y exists between i t s i n t a k e which i s e s s e n t i a l f o r the o r g a n i s m and the c o n c e n t r a t i o n s a s s o c i a t e d w i t h t o x i c e f f e c t s ( 1 7 ) . Growth i s r a p i d and many systems d e v e l o p t h e i r a d u l t c e l l number and c o m p o s i t i o n throughout the f i r s t y e a r o f l i f e . Optimal n u t r i t i o n i s thus most c r i t i c a l i n t h i s e a r l y p e r i o d . M i l k - the o n l y s o u r c e of f o o d f o r the o f f s p r i n g of a l l mammals i n the e a r l y months of l i f e - cannot meet the demands of o p t i m a l growth l a t e r on i n the f i r s t y e a r of l i f e . T h i s i s e s p e c i a l l y so w i t h the e s s e n t i a l elements such as i r o n and manganese whose low c o n t e n t i n m i l k (1823) does not meet the needs of a f a s t growing o r g a n i s m (24-^27). The e f f e c t o f m i l k upon i o n s a b s o r p t i o n from the i n t e s t i n a l t r a c t has been s t u d i e d e x t e n s i v e l y (28-33). The h i g h e r a b s o r p t i o n of i o n s i n the young than i n the a d u l t age (34-40) c o u l d be exp l a i n e d on the one hand by changes o c c u r i n g i n the i n t e s t i n a l membrane d u r i n g the p r o c e s s of a g i n g (41-45), or on the o t h e r hand, may be due to m i l k d i e t which i s d e p r i v e d of s e v e r a l e s s e n t i a l elements (28-33). Yet m i l k d i e t does not a f f e c t the m e t a b o l i s m of a l l ions e q u a l l y . For i n s t a n c e , a s e v e n - d a y - l o n g m i l k d i e t which n e i t h e r a l t e r s the t r a n s p o r t of c a l c i u m nor of l e a d i n s i x - w e e k - o l d female a l b i n o r a t s (46), s i g n i f i c a n t l y i n c r e a s e s the manganese t r a n s p o r t and r e t e n t i o n i n the duodenum of t h e s e a n i m a l s ( 4 7 ) . The l a t t e r e f f e c t c o u l d be e x p l a i n e d n e a t l y by the low manganese c o n t e n t of m i l k (48-52) were i t not t h a t m i l k f o r t i f i c a t i o n by manganese enhanced even f u r t h e r , h i g h l y s i g n i f i c a n t l y , the manganese t r a n s f e r and i n t e s t i n a l r e t e n t i o n ( 4 7 ) . Thus i t seems f a i r l y c o n c l u s i v e t h a t i t i s not manganese d e f i c i e n c y i n m i l k which i s r e s p o n s i b l e f o r an o v e r a l l enhancement of manganese t r a n s f e r i n t o and t h r o u g h the duodenal w a l l i n m i l k - t r e a t e d a n i m a l s . There i s a p o s s i b i l i t y t h a t some m i l k c o n s t i t u e n t s r e g u l a t e the a b s o r p t i o n of i o n s i n the i n t e s t i n e . In s t u d y i n g manganese metab o l i s m we t u r n e d t o the low i r o n c o n t e n t i n m i l k . I r o n has r e c e i v e d great a t t e n t i o n i n p e d i a t r i c n u t r i t i o n . The c o n c e r n has been to p r e v e n t the anemia caused by i r o n d e f i c i e n c y e a r l i e r o f t e n found i n childhood. Wide m i l k consumption by i n f a n t s and young c h i l d r e n makes t h i s food an a t t r a c t i v e v e h i c l e f o r i r o n f o r t i f i c a t i o n . I r o n - e n r i c h e d p r o p r i e t a r y m i l k s u b s t i t u t e s can a d e q u a t e l y p r e v e n t the anemia common t o i n f a n t s who s u b s i s t l a r g e l y on l o w - i r o n mother's or cow's m i l k ( 5 3 ) . Y e t , t h e r e i s i n s u f f i c i e n t knowledge about the b i o l o g i c a l a v a i l a b i l i t y of t h i s element, and the o p t i m a l l e v e l s have not y e t



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been adequately determined. There i s a r i s k of too high a l e v e l with putatively diverse e f f e c t s of increasing the dietary iron content (54-59). Further, since the amount of iron i n the diet and the iron body state influence the absorption of some essential and non-essential elements (60-71), the interaction between the minerals thay may have harmful effects on the body i s always possible. In view of a l l this we considered i t worthwhile to study the e f f e c t of iron upon manganese metabolism, following thus the l i n e i n i t i a t e d by some authors years ago (72-74). A l l our experiments were performed on r a t s . Although "man i s not a big r a t " (75) and extrapolation of experimental findings from animals to humans i s generally d i f f i c u l t , according to Mahoney and Hendricks (76) rats and humans respond q u a l i t a t i v e l y s i m i l a r l y to many dietary and physiological factors known to influence iron u t i l i z a t i o n . These authors have found iron absorption by rats to be highly correlated with that i n humans - a rather important finding for our (iron-manganese interactions) studies performed on r a t s . Studies In V i t r o The experimental animals were female albino r a t s , mostly f i v e weeks old. Iron-manganese interaction was studied on the everted duodenal segment (77) where the transport and absorption of the two metals per unit of time are higher than i n the more d i s t a l parts of the intestine (78-82). Manganese-54 and iron-59 were used as markers for their stable isotopes. Manganese Transport. Our f i r s t experiments showed that when milk was enriched with iron i n doses which equalized the d a i l y amount of iron received with milk to that of the stock diet (10 mg Fe/100 ml), the transduodenal transport of manganese became equal for animals fed on these two d i f f e r e n t diets (47). In other words, the stimul a t i v e effect of the o r i g i n a l , iron-deficient milk upon manganese transport disappeared completely, confirming thus the competition of iron and manganese at the expense of the l a t t e r (72-74). It comes to one's mind, of course, that the tissue deprived of manganese through a milk diet w i l l u t i l i z e more of the offered manganese. However, experiments with rats fed manganese-enriched milk resulted in more than a doubled transfer of manganese-54 (47) , showing thus that i t i s not the manganese deficiency i n milk which i s responsible for the enhanced manganese-54 transfer i n milk-fed animals. Moreover, when both manganese and iron content of milk were raised to the l e v e l i n the stock d i e t , the i n h i b i t o r y effects of iron upon manganese was s t i l l dominant (47). A l l t h i s indicates that there are some transport mechanisms common to iron and manganese so that i n the presence of both ions manganese w i l l be discriminated i n favor of iron. These findings suggest also that the pretreatment ^n vivo with p l a i n or enriched milk diet induces permeability changes i n the duodenal wall which p e r s i s t at least long enough for the manganese transport to be accomplished jln v i t r o . Dose Dependency. When the animals were fed only cow's milk f o r t i f i e d with different doses of ferrous sulphate (0.60-19.0 mg Fe/100 ml) for three days before k i l l i n g ^ manganese transfer and i t s



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duodenal r e t e n t i o n a l i k e f o l l o w e d the i r o n - d o s e dependency suggesti v e of a s a t u r a t i o n e f f e c t ( 8 3 ) . The i n h i b i t i o n had a m i l d l y exp r e s s e d maximum around 2.5 mg Fe/100 ml m i l k w i t h a l e v e l i n g of above 5 mg Fe/100 ml m i l k . The s i m p l e s t and most p l a u s i b l e r a t i o n a l i z a t i o n of t h i s e f f e c t was ( a g a i n ) t h a t t h e r e i s a compet i t i v e r e l a t i o n s h i p between i r o n and manganese f o r the c a r r i e r so t h a t i r o n i s the p r e f e r r e d i o n w i t h a p r o b a b l y h i g h e r a f f i n i t y f o r the b i n d i n g s i t e s w i t h i n the mucosa. To what e x t e n t the mechanism r e g u l a t i n g manganese a b s o r p t i o n i s dependent on the amount of i r o n i n the d i e t i s shown a l s o by the f o l l o w i n g . Even a t a t e n - f o l d i n c r e a s e i n d i e t a r y manganese (from 5.6 t o 56.0 mg Mn/100 g f o o d ) , at two c o n c e n t r a t i o n s of d i e t a r y i r o n (13 and 59 mg Fe/100 g f o o d ) , changes i n the duodenal t r a n s p o r t of manganese were o n l y m a r g i n a l l y s i g n i f i c a n t ( 8 4 ) . On the c o n t r a r y , f o r the animals f e d p l a i n i r o n d e f i c i e n t m i l k the r e s u l t s showed a marked dependence on manganese consumption, i . e . by i n c r e a s i n g manganese c o n c e n t r a t i o n i n m i l k (from 0.9 t o 9.6 mg/100 m l ) , t r a n s d u o d e n a l t r a n s f e r of manganese a l s o i n c r e a s e d . Similarly, the a d d i t i o n of manganese from 1.4 t o 10.0 mg/100 ml t o m i l k cont a i n i n g 5 or 20 mg of i r o n i n 100 ml s l i g h t l y reduced or l e f t unchanged the t r a n s f e r o f radiomanganese through the duodenal w a l l ( 8 5 ) . When the same amount of manganese was added t o m i l k which had not been e n r i c h e d w i t h i r o n , manganese t r a n s f e r s i g n i f i c a n t l y increased (47). A p o s s i b l e r e a s o n why manganese a d d i t i o n t o m i l k and s t o c k d i e t s g i v e s d i f f e r e n t r e s u l t s may w e l l be a d i f f e r e n c e s i n i r o n c o n t e n t between the two d i e t s . In the case o f an i r o n d e f i c i e n t d i e t ( m i l k ) , the ( r e g u l a t i o n o f ) manganese a b s o r p t i o n i s s e t o n l y by the manganese l e v e l of the d i e t . W i t h 5 and 20 mg Fe/100 ml the i r o n c o n t e n t i s w i t h i n i t s s a t u r a t i o n ("plateau") l e v e l ( 8 3 ) . I t thus i n f l u e n c e s manganese m e t a b o l i s m s i m i l a r l y t o the s t o c k d i e t . O b v i o u s l y , by i n c r e a s i n g the i r o n l e v e l i n m i l k above a t h r e s h o l d (2.5 mg/100 mg, 83) the t r a n s f e r and i n t e s t i n a l r e t e n t i o n of manganese become independent of b o t h the i r o n and manganese l e v e l s . Time Dependence. As the i n i t i a l i r o n d e f i c i e n c y (by m i l k f e e d i n g ) s t i m u l a t e s i r o n a b s o r p t i o n (53,86-90)> w h i c h i n t u r n may a f f e c t n e g a t i v e l y manganese a b s o r p t i o n (as d e s c r i b e d h e r e ) , the body i r o n s t a t e must a l s o be t a k e n i n t o a c c o u n t . I t i s t h e r e f o r e u s e f u l t o e s t a b l i s h data about the time f a c t o r , i . e . how l o n g the a n i m a l s can be t r e a t e d w i t h i r o n supplemented m i l k b e f o r e an a l t e r a t i o n i n manganese t r a n s p o r t i s observed and a l s o , how l o n g i t t a k e s f o r manganese t r a n s p o r t t o r e t u r n to normal once i r o n treatment has ceased. The r e l e v a n t e x p e r i m e n t s showed t h a t the i n h i b i t i o n o f manganese t r a n s f e r was p r e s e n t a f t e r one day of f e e d i n g on i r o n supplemented (10 mg Fe/100 ml) m i l k . The i n h i b i t i o n l e v e l e d o f f a l r e a d y a f t e r the second day of such f e e d i n g . The r e v e r s e e f f e c t - on w i t h d r a w i n g the supplementary i r o n ( i . e . 0.05 mg Fe/100 ml i n pure m i l k ) - was much s l o w e r , the i n c r e a s e i n manganese t r a n s p o r t h a v i n g become n o t i c e a b l e a f t e r the f o u r t h day ( 9 1 ) . The f a c t t h a t the onset o f i n h i b i t i o n of manganese t r a n s p o r t and r e t e n t i o n by i r o n i s f a s t e r t h a n i t s d i s a p p e a r a n c e may a l s o be due t o a h i g h e r a f f i n i t y of the c a r r i e r b i n d i n g s i t e s f o r i r o n t h a n f o r manganese. Once f i l l e d up w i t h i r o n these s i t e s w i l l r e s i s t i r o n d e f i c i e n c y f o r a l o n g e r time than they would need t o get



7. GRUDEN


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l o a d e d w i t h i r o n a f t e r an i r o n d e f i c i e n t s t a t e . As b o t h the appearance and d i s a p p e a r a n c e of the i n h i b i t o r y e f f e c t o f i r o n t a k e s days, i t i s l i k e l y t h a t the i n t e s t i n a l w a l l undergoes some r e v e r s i b l e changes. I r o n a b s o r p t i o n i s r e g u l a t e d by the c e l l s o f the i n t e s t i n a l mucosa a c c o r d i n g to the body's need (68,87-89,90,92). In i r o n d e f i c i e n c y the e p i t h e l i a l i r o n content i s reduced and i t s uptake as w e l l as t r a n s f e r t o the b l o o d i n c r e a s e d , w h i l e i n the l o a d e d s t a t e the s i t u a t i o n i s o p p o s i t e . Owing to the c h e m i c a l s i m i l a r i t y o f i r o n and manganese i t i s r e a s o n a b l e t o assume t h a t the i r o n b i n d i n g m a t e r i a l i n the i n t e s t i n a l mucosal c e l l s can a l s o b i n d manganese, e s p e c i a l l y i n the i r o n d e f i c i e n t s t a t e . A f t e r t h r e e days o f f e e d i n g w i t h a n i r o n - p o o r m i l k , i r o n d e p o s i t s i n the i n t e s t i n a l w a l l are m o s t l y used up by the body. As the b i n d i n g s i t e s i n v o l v e d i n the t r a n s f e r of m e t a l s from the mucosa to the s e r o s a show a g r e a t e r a f f i n i t y f o r i r o n than f o r manganese, the l a t t e r can r e p l a c e i r o n o n l y i n the i r o n d e f i c i e n t s t a t e . On the w h o l e , manganese r e t e n t i o n i n the i n t e s t i n a l w a l l i s f a r l e s s a f f e c t e d by i r o n than i t s t r a n s p o r t (47,91), w h i c h s u g g e s t s t h a t the b i n d i n g s i t e s f o r manganese (or i r o n ) t r a n s p o r t are not the same as f o r t h e i r r e t e n t i o n i n the mucosa. In o t h e r wards, the t r a n s p o r t b i n d i n g s i t e s are more s e n s i t i v e t o i r o n d e f i c i e n c y . N o t h i n g , o f c o u r s e , can be s a i d about a c t u a l m o l e c u l a r d i f f e r e n c e s between the two t y p e s of b i n d i n g s i t e s . The e f f e c t o f i r o n upon manganese t r a n s f e r was shown to be s i g n i f i c a n t l y h i g h e r i n the duodenum t h a n i n the jejunum or i l e u m . As f o r a n i m a l s ' age and sex i t was observed t h a t i r o n e f f e c t upon manganese t r a n s f e r and i n t e s t i n a l r e t e n t i o n was more pronounced i n the young (6-week-old) than i n the o l d r a t s (16- and 26-week o l d ) , and i n female t h a n i n male r a t s . S u r p r i s i n g l y , the e f f e c t was more dependent on sex t h a n on a n i m a l s ' age (Gruden, N., u n p u b l i s h e d d a t a ) . I r o n T r a n s p o r t . To g a i n a d d i t i o n a l i n s i g h t i n t o the iron-manganese i n t e r a c t i o n , the e x p e r i m e n t s were performed i n w h i c h the influence of m i l k , e i t h e r pure o r f o r t i f i e d w i t h i r o n and/or manganese, on i r o n t r a n s d u o d e n a l t r a n s p o r t was s t u d i e d ( 9 3 ) . The r e s u l t s c o r r o b o r a t e d our former i n t e r p r e t a t i o n . Namely, compared w i t h the s t a n d a r d d i e t as c o n t r o l , a t h r e e - d a y f e e d i n g w i t h cow's m i l k a l o n e r e s u l t e d i n a two and a h a l f t i m e s h i g h e r t o t a l t r a n s d u o d e n a l radioiron transport. The s t i m u l a t o r y e f f e c t o f m i l k was the same i f manganese was added to m i l k (1.1 mg Mn/100 m l ) , but d i s a p p e a r e d c o m p l e t e l y a f t e r the a d d i t i o n of 10 mg Fe/100 ml, a l o n e o r t o g e t h e r w i t h 1.1 mg manganese/100 m l m i l k . S i m u l t a n e o u s l y , t h e r e was no s i g n i f i c a n t change i n r a d i o i r o n uptake i n the i n t e s t i n a l w a l l . T h i s c o n f i r m s the assumption t h a t the b i n d i n g s i t e s f o r i r o n (and manganese) t r a n s p o r t are not the same as f o r t h e i r r e t e n t i o n i n the mucosa. These p r o c e s s e s c o u l d be r e garded as independent so t h a t changes i n one need not necessarily be accompanied by changes i n the o t h e r (73,74). Under i d e n t i c a l e x p e r i m e n t a l c o n d i t i o n s i r o n d e f i c i e n c y d e f i n a t e l y s t i m u l a t e s much more the t r a n s d u o d e n a l t r a n s p o r t and i n t e s t i n a l uptake o f radiomanganese than of r a d i o i r o n (47,93). T h i s c o u l d be e x p l a i n e d by the much more s t a b l e a b s o r p t i o n and o t h e r mechanisms i n the i n t e s t i n e f o r i r o n than f o r manganese. Whereas the h o m e o s t a s i s o f i r o n i s m a i n t a i n e d a t the l e v e l o f the i n t e s t i n a l


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tract (68,86,87,89,90,92), manganese homeostasis i s regulated (also) at the excretion l e v e l no matter how much manganese has been absorbed from the intestine (8,94-97). The fact that manganese had no effect on iron transport could be explained by different K values for iron and manganese (73). This again suggests that the shared i n t e s t i n a l transport system shows less a f f i n i t y for manganese than for iron and explains a greater i n h i b i tory effect of iron on manganese absorption than of manganese on iron absorption. It may also be that there exists iron-binding s i t e s which i f free from i r o n could be used to manganese transport and that other manganese-binding s i t e s are present i n much greater abundance but are used exclusively for manganese ions. The l a t t e r conclusion, reached also for Forth and Rummel (98) i s strongly supported by the fact that the enrichment of iron-poor milk with manganese enhances the transfer and i n t e s t i n a l retention of radiomanganese but does not affect iron transport (93). Two conclusions which could have p r a c t i c a l importance may be derived so f a r : 1) i n combating neonatal iron deficiency, by increasing simultaneously iron and manganese content i n milk i t might be possible to diminish the r i s k of manganese deficiency and 2) milk does not seem to be the best means of a d d i t i o n a l n u t r i t i o n in exposure to manganese.


m

Studies In Vivo In view of l i t e r a t u r e data and our (in v i t r o ) results on i r o n manganese interaction, we considered i t worthwhile to study the e f f e c t of iron on manganese metabolism i n very young rats when absorptive, homeostatic and competitive mechanisms i n the i n t e s t i n a l tract are not yet functioning properly or are i n a developing phase. We performed experiments to see what role iron dose, duration of treatment and animals age have i n iron-manganese competition at an early period of rat's l i f e . Five- to 21-day-old white rats were used. The animals were placed into groups according to the amount of iron they had received in iron supplemented cow's milk for either one ("non-pretreated") or four days ("pretreated"). Iron doses were from 52 to 1000 yg Fe/ml milk. Radioisotopes (Mn-54 or Fe-59) were always administered by the a r t i f i c i a l "drop-by-drop" feeding procedure (99). The radioa c t i v i t y was determined i n selected organs ( l i v e r , kidney, spleen, brain, femure, i n t e s t i n a l t r a c t , stomach) i n addition to measurements of the whole body and carcass. 1

Sucklings. Although the i n h i b i t o r y e f f e c t of iron on manganese absorption i s recognized (2,47,72-74,83,91,100), i t i s not known when p r e c i s e l y i t sets i n . It seems that i n the neonatal, six-day-old rats the competition between iron and manganese absorption i s not yet developed. Namely, the addition for one (101) or four days (102) of low, p h y s i o l o g i c a l amounts of iron to milk diet (50 or 100 yg Fe/ml) did not appreciably decrease manganese absorption. Moreover, i n neonatal rats treated with these iron doses for four days, manganese54 values i n the whole body (absorption), intestine, l i v e r and kidneys were even greater by 10 to 52 percent than i n the controls receiving p l a i n cow's milk (102). No interpretation can be offered why and how the introduction of low iron doses increased



7. GRUDEN


73

radiomanganese absorption at the same dietary manganese l e v e l for a l l animal groups. However, when a dose of 200 yg Fe/ml or higher (410-1000 yg Fe/ ml) was administered even on a single day, i t caused i n these s i x day-old rats a s i g n i f i c a n t and mainly dose-dependent diminution of manganese absorption and organ uptake, with the exception of the l i v e r (103). Our explanation i s that a) at that early age the lower i r o n doses (below 200 yg Fe/ml) have no e f f e c t whatsoever on the route(s) of manganese transport and b) that owing to lack of homeos t a t i c iron regulation at that age (104) the large(r) amounts of iron introduced (doses of 200, 410 and 1000 yg Fe/ml) can block the manganese pathways. The l a t t e r conclusion i s corroborated by the enhanced iron retention (104) and the diminished manganese one i n the l i v e r and i n t e s t i n e (103). In other words, i n the absence of a regulatory mechanism for iron absorption, i t s enhanced uptake owing to high amounts of iron added to the milk diet eliminates manganese. This i n turn implies that the organism at such an early age i s much more prone to accept iron at the expense of manganese. Weanlings. In three-week-old rats i . e . , at an age when some h i s t o biochemical changes take place i n the i n t e s t i n a l tract (41,42,45,105, 106) the e f f e c t of iron on manganese metabolism i s somewhat d i f f e r e n t from that i n neonatal animals. According to some authors (107) the iron content of the weanling diet plays even a c r i t i c a l role i n terminal maturation of rat small i n t e s t i n e . Anyhow, doses of 100 and 200 yg Fe/ml, administered on a single day enhanced s i g n i f i c a n t l y (by 30-40 percent) radiomanganese absorption i n weanling r a t s , thus influencing also manganese d i s t r i b u t i o n within t h e i r organism. At higher iron concentrations (410 and 1000 yg Fe/ml), a s i g n i f i c a n t drop (25-35 percent with respect to the controls fed with no addit i o n a l iron i n milk) i n manganese absorption was observed (103). I t thus appears that i n the weaning age manganese does not have to compete with iron i f iron doses can be controlled by the homeostatic mechanism. However, with the dose of 410 yg Fe/ml iron-manganese competition sets i n abruptly, as (probably) the s t i l l large absolute amounts of iron block the manganese pathways to an appreciable degree. It must be emphasized that the homeostatic regulation of iron absorption i s e f f i c i e n t i n weaning but not i n neonatal rats (104). In consequence, large amounts of iron prevent manganese transport i n neonatals. The same i s true of the weanlings but at the higher iron doses, when the homeostatic iron regulation cannot suppress iron amounts below the threshold causing competition with manganese. I t turns out that the dose of 410 yg Fe/ml milk i s above the threshold irrespective of whether i t i s applied during a four-day treatment (4 x 100 yg Fe/ml, 108), or given on a single day (103). It i s concluded that the mechanisms which regulate i r o n manganese competition, although operating i n the intestine of weanl i n g r a t s , i n order to function properly need to be activated either by iron doses above a certain threshold (103) or by some duration (four days - i n our case, 108) of treatment with lower iron doses. The Development of Iron-Manganese Competition. The competitive effect of iron upon manganese absorption depends not only on the duration of iron treatment (101,102,108) and on the iron dose



74

NUTRITIONAL BIOAVAILABILITY OF

MANGANESE

a d m i n i s t e r e d ( 1 0 3 ) , but a l s o , t o a g r e a t e x t e n t on t h e a n i m a l s age (108). The q u e s t i o n remains whether t h i s e f f e c t i s t r i g g e r e d o f f a b r u p t l y i n the r a t ' s weaning r:ge, o r whether i t i s d e v e l o p i n g g r a d u a l l y from t h e n e o n a t a l t i l l t h e weaning p e r i o d . Experiments performed on 8,11,14 and 17-day-old a n i m a l s t o g e t h e r w i t h t h e e a r l i e r r e s u l t s on f i v e - d a y - (102) and t h r e e - w e e k - o l d r a t s (108) i n d i c a t e t h a t manganese a b s o r p t i o n does n o t s i g n i f i c a n t l y d i f f e r between t h e c o n t r o l ( p l a i n m i l k d i e t ) and i r o n - t r e a t e d r a t s (100 yg Fe/ml d i e t - d u r i n g f o u r days) u n t i l t h e 17th day o f age. From t h e n on i t s h a r p l y d e c r e a s e s i n t h e i r o n - p r e t r e a t e d a n i m a l s t o a t t a i n i n t h e t h i r d week as much as 50 p e r c e n t l o w e r v a l u e s t h a n i n c o n t r o l a n i m a l s ( 1 0 9 ) . The abrupt d i m i n u t i o n o f manganese r e t e n t i o n (as w e l l as t h a t o f i r o n - 5 9 i n i d e n t i c a l e x p e r i m e n t s , (110) i n i r o n p r e t r e a t e d a n i m a l s between t h e 17th and 2 1 s t day of l i f e i s l i k e l y to be due t o t h e a l t e r a t i o n s t a k i n g p l a c e i n t h e i n t e s t i n a l t r a c t of the r a t a t t h a t age. Having i n mind t h a t t h a t i s a l s o t h e time o f weaning, one i s i m p e l l e d t o t a k e i n t o account t h e type o f food consumed by t h e a n i m a l s . However, our w e a n l i n g r a t s s w i t c h e d over from mother's t o cow's m i l k and n o t t o t h e s t a n d a r d l a b o r a t o r y f o o d . Thus, any major e f f e c t due t o a change o f food c o n s i s t e n c y can be e l i m i n a t e d . I n a l l l i k e l i h o o d i t i s t h e h i s t o b i o c h e m i c a l change i n t h e i n t e s t i n e t h a t f a c i l i t a t e s t h e onset o f iron-manganese i n t e r a c t i o n w i t h i n t h i s b r i e f p e r i o d of l i f e . Summarizing, i t may be c o n c l u d e d t h a t t h e mechanisms r e g u l a t i n g iron-manganese i n t e r a c t i o n become o p e r a t i v e i n t h e t h i r d week o f the r a t ' s l i f e , i . e . , a t t h e same time when t h e r e g u l a t i o n o f i r o n a b s o r p t i o n i s f u l l y a c t i v a t e d . E x p e r i m e n t a l e v i d e n c e suggests t h a t the onset o f t h i s r e g u l a t i o n i s n o t provoked by a change from m i l k to s o l i d f o o d . I r o n and Cadmium-Manganese

Interactions

The e f f e c t o f i r o n on cadmium-manganese i n t e r a c t i o n w i l l be b r i e f l y d e a l t w i t h . The d a t a about t h e e f f e c t o f cadmium on manganese m e t a b o l i s m a r e r a t h e r s c a n t y (78,111-114). N e v e r t h e l e s s , some d a t a c l e a r l y show t h a t manganese t r a n s f e r through and i t s r e t e n t i o n i n the r a t ' s duodenal w a l l a r e s i g n i f i c a n t l y depressed i n t h e p r e s e n c e of cadmium ( 1 1 5 ) . By t h e s i m u l t a n e o u s a d d i t i o n of i r o n t o t h e a n i m a l s ' m i l k d i e t t h e a c t i o n o f i r o n and cadmium upon manganese a b s o r p t i o n becomes s y n e r g i s t i c . T h i s i s s u b s t a n t i a t e d by t h e o b s e r v a t i o n t h a t t h e a l r e a d y e x i s t i n g i n h i b i t o r y e f f e c t o f cadmium i s enhanced by 10 t o 60 p e r c e n t i n t h e p r e s e n c e o f i r o n and, i n a d d i t i o n , t h a t i t becomes n o t i c e a b l e even a t such low doses o f cadmium at which o t h e r w i s e t h e r e i s none (Gruden, N., P r o c . 5 t h I n t . Symp. Trace Elem., Jena 1986, i n p r e s s ) . A s a t u r a t i o n e f f e c t i s i n d i c a t e d i n t h a t i r o n enhances i d e n t i c a l l y t h e cadmium i n h i b i t o r y e f f e c t upon manganese a b s o r p t i o n i r r e s p e c t i v e o f t h e cadmium dose. I n a d d i t i o n , t h e i r o n dose does not a l t e r o n l y the a l r e a d y s t r o n g e f f e c t o f h i g h cadmium dose. F u r t h e r m o r e , w i t h i n a span o f 5.0-15.0 mg Fe/100 ml i r o n has an e q u a l e f f e c t upon cadmium a c t i o n , w h i l e below 2.5 mg Fe/100 ml i t does n o t a l t e r t h e e f f e c t of cadmium a t a l l . This i s y e t another i n d i c a t i o n o f i r o n s a t u r a t i o n a t a l e v e l above 5.0 mg Fe/ml m i l k , as o b s e r v e d e a r l i e r ( 8 3 ) .


7. G R U D E N


75

A plausible r a t i o n a l i z a t i o n would be that there i s a competition for the transport route through the i n t e s t i n a l wall between cadmium and manganese on the one side, and between iron and manganese on the other. The competition, i . e . , absorption i n the i n t e s t i n a l t r a c t , depends upon the r e l a t i v e concentration of these ions and k i n e t i c s of and a f f i n i t y for their i n t e r a c t i o n with the binding s i t e s i n the i n t e s t i n a l mucosa.


Concluding Remarks During the past f i f t e e n to twenty years observations have accumulated to an extent which enables us to grasp the framework of a complex relationship between two essential elements, iron and manganese. The competition between the two for the transport through the i n t e s t i n a l wall, i . e . , absorption and their retention within the various organs must be viewed with regard to the evolving o v e r a l l homeostatic mechanism on the one hand, and the histobiochemical a l t e r a t i o n s of the tissues on the other. It has thus been e s t a b l i s h ed that the iron-manganese competition i n the i n t e s t i n e at the expense of manganese sets i n rather suddenly between the 17th and 21st day of the rats l i f e . The reversal of iron-manganese e f f e c t s in neonatal to those i n weanlings i s not due to the change from l i q u i d (milk) to s o l i d food, but (most probably) to the f u l l a c t i vation of the mechanism regulating iron absorption. The competition is evident with iron doses that can be controlled by the homeostatic mechanism, but the difference i n the homeostatic s i t e s for iron and manganese must be taken into account i n r a t i o n a l i z i n g their i n t e r play. The pretreatment in vivo with p l a i n or enriched milk diet i n duces changes i n the permeability of the i n t e s t i n a l wall which pers i s t at least long enough for manganese transport to be accomplished in v i t r o . There i s obviously a competitive relationship between iron and manganese for the c a r r i e r so that iron i s the preferred ion with a probably higher a f f i n i t y for the binding s i t e s within the mucosa. This also explains the fact that the i n h i b i t i o n of manganese transport and retention evolves f a s t e r on iron a p p l i c a t i o n , than i t disappears a f t e r iron withdrawal. As both the appearance and d i s appearance of the i n h i b i t o r y e f f e c t of iron take days, i t i s l i k e l y that the i n t e s t i n a l wall undergoes some r e v e r s i b l e changes. Manganese retention i n the i n t e s t i n a l wall i s far less affected by iron than i t s transport, which suggests that the binding s i t e s for manganese (or iron) transport are not the same as for their retention i n the i n t e s t i n a l mucosa. In other words, the transport binding s i t e s are more sensitive to iron deficiency, which means that iron deficiency stimulates much more the transduodenal transport of manganese (and iron) than their i n t e s t i n a l uptake. From the p r a c t i c a l standpoint of p a r t i c u l a r importance i s that i t i s not the manganese deficiency i n milk that i s responsible for an o v e r a l l enhancement of manganese transfer into and through the duodenal wall i n milk-treated animals. I t i s rather the a v a i l a b i l i t y to manganese of the i r o n - c a r r i e r s i t e s owing to the low iron content of milk. Hence, milk does not seem to be the best means of additional n u t r i t i o n i n exposure to manganese. On the other hand, i t might be possible to diminish the r i s k of manganese deficiency i n


NUTRITIONAL BIOAVAILABILITY OF MANGANESE

76

combating n e o n a t a l i r o n d e f i c i e n c y by i n c r e a s i n g s i m u l t a n e o u s l y i r o n and manganese c o n t e n t i n m i l k . I n t h e f u t u r e r e s e a r c h w i l l have t o be engaged i n e x p l a i n i n g a t the m o l e c u l a r l e v e l why i r o n i n h i b i t s manganese t r a n s f e r and a b s o r p t i o n i n the i n t e s t i n a l t r a c t .


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78 68. 69. 70. 71. 72. 73.


74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. 85. 86. 87. 88. 89. 90. 91. 92. 93. 94. 95. 96. 97. 98. 99. 100. 101. 102. 103. 104. 105. 106. 107.

NUTRITIONAL BIOAVAILABILITY OF MANGANESE Ragan, H.A. S c i . Total Environ. 1983, 28, 317. Leon, L.; Johnson, D.R. J . Toxicol. Environ. Health 1985, 15, 687. Becker, G.; Huebers, H . ; Rummel, W. Blut 1979, 38, 397. Sephton, R.; Martin, J.J. Br. J. Radiol. 1980, 53, 572. Pollack, S.; George, J . N . ; Reba, R.C.; Kaufman, R.M.; Crosby, W.H. J . Clin. Invest. 1965, 44, 1470. Thomson, A.B.R.; Olatunbosun, D.; Valberg, L . S . ; Ludwig, J . J . Lab. Clin. Med. 1971, 78, 642. Thomson, A.B.R.; Valberg, L.S. Am. J. Physiol. 1972, 223, 1327. Oser, B.L. J . Toxicol. Environ. Health 1981, 8, 521. Mahoney, A.W.; Hendrics, D.G. Nutr. Res. 1984, 4, 913. Wilson, T.H.; Wiseman, G. J . Physiol. (Lond.) 1954, 123, 116. Sahagian, B.M.; Harding-Barlow, I.; Perry, H.M. Jr. J . Nutr. 1966, 90, 259. Ansari, M.S.; M i l l e r , W.J.; Neathery, M.W.; Lassiter, J.W.; Gentry, R.P. Nutr. Reports Int. 1977, 15, 37. Howard, J.; Jacobs, A. B r i t . J . Haematol. 1977, 23, 595. Gruden, N . ; Buben, M. Iugoslav. Physiol. Pharmacol. Acta 1978, 14, 83. Richter, G.W.; Lee, Y.H. Experientia 1982, 38, 583. Gruden, N. Nutr. Metab. 1977, 21, 305. Gruden, N. Period. B i o l . 1979, 81, 567. Gruden, N . ; Buben, M. Period. B i o l . 1980, 82, 9. Charlton, R.W.; Jacobs, P . ; Torrance, J.D.; Bothwell, T.H. J . Clin. Invest. 1965, 44, 543. Narasinga Rao, B.S. Br. Med. B u l l . 1981, 37, 25. Huebers, H . ; Finsh, C.A. Semin. Hematol. 1982, 19, 3. Refsum, S.B.; Schreiner, B.B. Scand. J . Gastroenterol. 1984, 19, 867. Nathanson, M.H.; Muir, A . ; McLaren, G.D. Am. J. Physiol. 1985, 245, G439. Gruden, N. Nutr. Reports Int. 1977, 15, 577. Finch, C.A.; Huebers, H.A. Clin. Physiol. Biochem. 1986, 4, 5. Gruden, N. Nutr. Reports Int. 1979, 19, 69. M i l l e r , W.J. Fed. Proc. 1973, 32, 1915. Klaassen, C.D. Toxicol. Appl. Pharmacol. 1974, 29, 458. Kojima, S.; H i r a i , M . ; Kiyozumi, M . ; Sasawa, Y . ; Nakagawa, M . ; Shin-o, T. Chem. Pharm. Bull. 1983, 31, 2459. Symonds, H.W.; H a l l , E.D. Res. Veter. S c i . 1983, 33, 5. Forth, W.; Rummel, W. Physiol. Rev. 1973, 53, 724. Kostial, K . ; Simonovic, I.; Pisonic, M. Nature (London) 1967, 215, 1181. Khandelwal, S.; Asquin, M.; Tandon, S.K. B u l l . Environ. Contam. Toxicol. 1984, 32, 10. Gruden, N. Reprod. Nutr. Develop. 1980, 20, 1539. Gruden, N . ; Buben, M. Nutr. Reports Int. 1981, 24, 943. Gruden, N. Nutr. Reports Int. 1986, Gruden, N. Nutr. Reports Int. 1986, 33, 693. Baintner, K . , Jr.; Veress, B. Experientia 1970, 26, 54. Forbes, G.B.; Reina, J.C. J . Nutr. 1972, 102, 647. Buts, J . P . ; Delacroix, D . L . ; Dekeyser, N . ; Paquet, S.; Horsman, Y . ; Boelens, M.; et al. Am. J. Physiol. 1984, 246, G745.


7. GRUDEN 108. 109. 110. 111. 112. 113.


114. 115.


79

Gruden, N. Nutr. Reports Int. 1982, 25, 849. Gruden, N. Nutr. Reports Int. 1984, 30, 553. Gruden, N. Nutr. Reports Int. 1983, 28, 473. Sahagian, B.M.; Harding-Barlow, I.; Perry, H.M., Jr. J . Nutr. 1967, 93, 291. Stacey, N.H.; Klaassen, C.D. J. Toxicol. Environ. Health 1981, 7, 149. Suzuki, K.T.; Yaguchi, K.; Onuki, R.; Nishikawa, M.; Yamada, Y.K. J. Toxicol. Environ. Health 1983, 11, 713. Jacobs, R.M.; Lee Jones, A.O.; Spivey Fox, M.R.; Lener, J. Proc. Soc. Exp. Biol. Med. 1983, 172 34. Gruden, N. In Heavy Metals in the Environment, Lekkas, T.D., Ed.; Athens, 1985; Vol. 1, p. 676.

RECEIVED April 29, 1987


Nutritional Bioavailability of Manganese - American Chemical Society

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